The Solid-state transformer (SST) has been proposed by researchers to replace the regular distribution transformer in the future smart grid. The SST provides ports for the integration of storage and distributed generation (DG), e.g., photovoltaic (PV), and enables the implementation of power quality features. This paper proposes a SST topology based on a quad-active-bridge (QAB) converter which not only provides isolation for the load, but also for DG and storage. A gyrator-based average model is developed for a general multiactive-bridge (MAB) converter, and expressions to determine the power rating of the MAB ports are derived. These results are then applied to analyze the QAB converter. For the control of the dc-dc stage of the proposed QAB-based SST integrating PV and battery, a technique that accounts for the cross-coupling characteristics of the QAB converter in order to improve the regulation of the high-voltage-dc link is introduced. This is done by transferring the disturbances onto the battery. The control loops are designed using single-input single-output techniques with different bandwidths. The dynamic performance of the control strategy is verified through extensive simulation and experimental results.

In this paper, a comparison of six representative topologies for the implementation of Solid State Transformers (SST) is performed. The objective is to help identify the most suitable topology capable of supporting additional functionalities as compared to a regular transformer, e.g. on-demand reactive power support to grid, voltage regulation, and current limiting. The comparison is based on switch loss, switch count, control characteristics and supported functionalities. It has been concluded that a three-stage configuration comprising distinct AC-DC, DC-DC and DC-AC stages results in the most suitable implementation. A Simulink model corresponding to this three-stage configuration is developed to demonstrate the desired characteristics and functionalities of the SST.

A simple control technique for a three-port DC-DC converter based PV system with storage is presented herein. The controller takes advantage of the fast response and cross coupling characteristics of the selected three port topology itself to obtain transient ride through support from the storage while using traditional control design techniques, e.g. SISO control design and Feedforward compensation. A gyrator average model for the selected three port topology is also presented. The performance of the controls is verified through simulations.

This paper addresses the control design for a three-stage solid stage transformer (SST). When two or more independently controlled converter stages are cascaded, which is the case for the three-stage SST, the interaction among the stages can lead to instability. Normally, the input and output impedances of the cascaded stages need to be examined according to the impedance criterion to ensure stability. In this paper, a novel energy-based control design method is proposed for the three-stage SST that enables decoupled control design for the rectifier and DC-DC stages, which avoids the need for the impedance checking and hence significantly simplifies the control design. The energy-based concept also works well with the power control methods commonly used such as those based on the DQ frame or the instantaneous reactive power (IRP) p-q theory, which allows for simple reactive power or power factor control. The design of the various control loops of the SST is described in detail in this paper and validated through simulations.

In this paper, the design of a linear quadratic regulator (LQR) controller for the DC-DC stage of a Solid State Transformer (SST) based on a quad-active-bridge (QAB) to integrate both photovoltaic (PV) power generation and battery energy storage is presented. The gyrator-based average model is used for deriving the state-space representation of the plant. The dynamic performance of the designed controller is verified through extensive simulation of the switching model and validated with experimental results.